PBL 3

Question 1

What is the Ideal Gas Law?

Answer 1

For a dry gas:
PV = nRT or P=nRT/V.
At constant T and V: P is proportional to number of moles. P1V1=P2V2=nRT

Question 2

What is Dalton’s law?

Answer 2

Each gas in a dry mixture exerts a partial pressure proportional to its fractional share of the total volume. Partial pressure of a gas is dependent on the number of gas molecules.

Question 3

What is the partial pressure of O2 in the atmosphere (sea level)?

Answer 3

21%

Question 4

Why are partial pressures important?

Answer 4

Because from outside the body to the mitochondria in cells, partial pressure of O2 varies. This leads to gradients which allow its movement through from atmosphere to lungs to blood to tissues (and most importantly for diffusion). Summary: partial pressure gradients drive diffusion.

Question 5

What is Boyle’s law?

Answer 5

P is equivalent to 1/V. At constant temperature, the pressure exerted by a constant number of gas molecules in a container is inversely proportional to the volume of the container. P1xV1 = P2xV2

Question 6

What is Fick’s law?

Answer 6

Rate of diffusion = SA x 1/thickness x diffusibility x partial pressure gradient

Question 7

What is the partial pressure of O2 and CO2 in the atmosphere?
In the lungs?
At the start of the capillary and at the end (after exchange has happened)

Answer 7

Atmosphere = PAO2 21kPa and PACO2 = 0
Air in lungs = PA02 13kPa and PAC02 5kPa
At start of alveolar capillary = PV02 5kPa, PVC02 = 6kPa
At the end of the alveolar capillary = PA02 13kPa, PAC02 5kPa